Nanowires
Semiconductor nanowires (NWs) with ultrathin diameter below the exciton Bohr radius, especially those with magic-size (i.e., less than 2 nm) diameter, have attracted significant interest in the past few years because of their predicted unique quantum confinement effects, quantum conductance, ballistic conduction, low thermal conductivity, increased surface area properties, and potential applications in thermoelectric devices, sensors, catalysts, and other nanodevices. Spherical magic-size semiconductor clusters (or ultra-small nanocrystals) with a well-defined number of atoms have been extensively prepared by various techniques, however, ultrathin semiconductor NWs with magic-size diameter have been difficult to achieve.
Zinc sulfide (ZnS), an important semiconductor material with a direct band gap of 3.6 eV at room temperature and a large exciton binding energy of 40 meV, is widely used in lasers, electroluminescent devices, flat panel displays, field emitters, infrared windows, and UV-light detectors. To the best of our knowledge, there has been no report describing high quality ZnS NWs with diameters below 2 nm.
Doping can enhance the properties of semiconductors by providing a powerful method to control their significant optical, electronic, transport, and spintronic properties. Mn-doped zinc chalcogenide quantum dots (QDs) have been explored as alternatives to CdSe QDs. Methods for the synthesis of high-quality Mn-doped ZnS QDs, characterized by sharp exciton absorption peaks, finely tunable and uniform diameters, tunable doping levels, and high quantum yields are still needed.
Quantum Dots
There are currently two grand challenges in the field of colloidal quantum dots (QDs, or semiconductor nanocrystals) based nanotechnology: one is to achieve robust non-blinking QDs and the other is to assemble different QDs of unique optical properties into hierarchically organized nanoarchitectures with control at single particle levels.
Nevertheless, there are still some challenges: 1) in synthesizing non-blinking or less blinking QDs of tunable multi-color emissions from blue to near infrared spectral range; 2) to achieve water-soluble nonblinking or less blinking QDs to conjugate with biomolecules, so they can be widely used for biological imaging applications; 3) more fundamental understanding and characterization of the non-blinking behavior are needed which requires synthesis of non-blinking QDs of different composition and optical properties; 4) efforts are greatly needed to achieve hierarchical assembly of these QDs into addressable architectures so it could provide a solid platform for systematic understanding of QD-QD interactions (e.g. Fluorescent Energy Transfer between QDs) and fabrication of QD based nanodevices for applications in biosensing and imaging.
Quantum Sheets and Ribbons
Tin sulfide (SnS) is an important main-group IV-VI (IV=Ge, Sn, Pb; VI=S, Se, Te) compound received significant attention recently due to its narrow band gap and rich electronic and optical properties. SnS is also known as inexpensive, naturally abundant, environmentally-benign, and heavy-metal-free (i.e., free from Cd, Pb, and Hg). Theoretical calculations indicate that SnS possesses all the qualities required for efficient absorption of solar energy, suitable for incorporation into clean energy conversion cells. Its other useful properties, e.g., photoconducting, photocatalytic and Peltier effect, make them promising candidates for diverse applications such as thermoelectric cooling, thermoelectric power generation, and near-infrared photo-electronics. All of the above applications would greatly benefit from the availability of the synthesis of SnS nanostructures with well-defined crystalline, sizes, and shapes in large quantities. However, synthesis of high quality SnS nanostructures is still a great challenges, relative to what has been achieved for both PbS and PbSe.